Olmesartan medoxomil is a new angiotensin-2 receptor blocker (ARB). Its pharmacokinetics in hemodialysis patients has not been investigated. We evaluated the pharmacokinetics of olmesartan medoxomil in six patients on maintained hemodialysis. We divided these six patients into two groups; one group (n = 3) took the drug when hemodialysis started (HD day group), and the other group (n = 3) took in the morning on non-dialysis day (non HD day group). In each group, plasma concentrations of olmesartan were evaluated seven points after drug administration. In each point, blood pressure and heart rate were also measured. On HD day group, plasma concentrations in upstream of dialyser were compared with those in downstream of dialyser in three points. The area under the plasma concentration-time curve (AUC) in HD day group had no remarkable difference from those in non-HD day group. Another pharmacokinetic parameter, such as maximum plasma drug concentration (C (max)), biological half-life (t (1/2)) and time to reach C (max) (t (max)), were almost similar in both groups. Blood pressure and heart rate showed the same consequence as well. This result suggests that plasma concentration of olmesartan medoxomil does not decrease during hemodialysis, and that it is not necessary to change prescription on hemodialysis day or not.